Valve device

ABSTRACT

The invention relates to a valve device comprising a valve housing ( 2 ) and a valve piston ( 4 ) arranged in an axially displaceable manner in a piston bore ( 3 ) of the valve housing ( 2 ), via which valve piston a first load connection (A) and a second load connection (B) can alternately be connected to a pressure connection (P) and to a tank connection (T 1,  T 2 ) by the action of a first solenoid magnet ( 5 ) and a second solenoid magnet ( 6 ), a pilot control unit ( 7 ) being provided, which comprises a first pilot control chamber ( 8 ) that pressurizes a first piston back side ( 9 ) of the valve piston ( 4 ) and a second pilot control chamber ( 10 ) that pressurizes a second piston back side ( 11 ) of the valve piston ( 4 ), the first and second pilot control chambers ( 8, 10 ) being connectable via a respective fluid-conducting connection ( 12, 13 ) to the pressure connection (P), a first pilot control piston ( 14 ) and a second pilot control piston ( 15 ) being provided, which release or close a fluid-conducting connection ( 16, 17 ) between the pilot control chambers ( 8, 10 ) and the tank connection (T 1,  T 2 ), respectively, characterized in that at least one pilot control piston ( 14, 15 ) comprises a ring channel ( 19 ) on the outer circumferential surface ( 20 ) thereof, which piston controls a fluid-conducting connection ( 16, 17 ) between the respective pilot control chamber ( 8, 10 ) and the respective associated tank connection (T 1,  T 2 ).

The invention relates to a valve device comprising a valve housing and a valve piston which is arranged to be able to move axially in a piston bore of the valve housing and via which a first load connection and a second load connection can be alternately connected to a pressure connection and to a tank connection. The valve piston can be moved out of a centered, middle rest position for connecting the first load connection to the pressure connection and the second load connection to the tank connection in a first direction and, for the reversed fluid-conducting connection, the connections can be moved in an opposite direction, there being a pilot control unit which has a first pilot chamber which pressurizes a first piston back side of the valve piston, and which has a second pilot chamber which pressurizes a second piston back side of the valve piston, and the first and second pilot chamber with one fluid-conducting connection each can be connected to the pressure connection, and there being a first pilot piston and a second pilot piston which clear or block one fluid-conducting connection at a time between the pilot chambers and the tank connection, and the pilot control unit being made in the manner of a spool valve.

Valve devices are available in a plurality of embodiments, for example, as multiport valves. In conjunction with a so-called electromagnetic actuation, they are an important component of so-called proportional valve technology. This technology is essentially characterized in that an electrical input signal as voltage is converted into an electrical current with an electronic amplifier of the corresponding voltage level. A proportional solenoid as a switching magnet generates the output quantities force or path proportionally to this electrical current.

These quantities are used as the input signal for the valve device or the hydraulic valve and, correspondingly proportional thereto, for a specific volumetric flow or a specific pressure. For the respective actuated load, and a working element which has been actuated with it on a machine, in addition to influencing the direction of movement this means the possibility of continuously influencing the speed and force. At the same time, according to a corresponding time characteristic, for example, change of the volumetric flow over time, acceleration or deceleration can be continuously influenced. Depending on which function is being emphasized, that is, the path function, the flow function, and/or the pressure function, proportional hydraulics is used in directional valves, flow control valves, or so-called pressure valves.

The technical advantages of the proportional valve technology include controlled actuation transitions, continuous control of the setpoints, and the reduction of the hydraulic apparatus for certain control tasks. Furthermore, with proportional valves, prompt and exact sequences of motion are possible with simultaneously improved accuracy of the control processes.

It has been shown, however, that the known valve device solutions still leave something to be desired in the field of proportional valve technology for some control tasks, such as in double-acting hydraulic working cylinders in which the triggering takes place for positioning tasks while avoiding mechanical coupling elements, especially with respect to the operational reliability of the overall system as well as prompt response behavior.

DE 43 19 162 A1 discloses a valve device with two opposing solenoids which are connected to a valve housing, with fluid connection sites mounted in the valve housing in the form of at least one pump connection P, at least two load or user connections A, B, and at least two tank connections T1 and T2, and with a valve piston which has radial projections which can each be assigned to one fluid connection site A, B, P, T1, T2 at a time in the valve housing and with fluid-conducting paths between the projections, in a neutral position the path to the respectively assignable user connection A, B being blocked in part or in full, or with the user connections A, B cleared, the respective pump connection P is completely blocked by the assignable projection. The known solution relates to a hydraulic valve which can be used for controlling a hydraulic actuator in a roll stabilization system of a motor vehicle. In the known solution, however, it is not precluded that possible disturbance variables will adversely affect the hydraulic valve system.

DE 31 19 445 A1 discloses an electrohydraulic control valve with a main housing as a valve housing which surrounds an axial bore in which a valve element as valve piston can be moved. The ends of the valve piston consist of a magnetizable material, and solenoid devices are assigned to the housing part as the actuating apparatus on the outer ends of the axial bore in order to pull the valve element in the direction of one end of the axial bore or the other by excitation of one solenoid device or the other. For compensation of disturbance variables, this known solution has pressure detecting pistons which extend through the valve piston on its two ends. In spite of the possibility of influencing the disturbance variables via the respective pressure detecting piston, this known solution leaves much to be desired with respect to complete compensation for such disturbances.

DE 600 16 510 T2 describes a piloted directional valve with position determination, with a housing that has a number of connections and a piston bore in which each connection discharges. A valve piston is guided to be able to move axially in the piston bore to change the flow paths between the connections. Furthermore, there are to some extent complex control means for controlling the valve piston, with the control means comprising a piston on each side of the valve piston and one or two pilot valves for setting the valve piston by control of the pilot fluid acting on the pistons. Furthermore, there is a magnet which is attached to one side of the valve piston such that it can be moved in synchronous operation with the valve piston. The magnet is arranged such that it borders at least one site of the valve piston. There is furthermore a magnetic sensor which is installed such that it detects the magnetic force of the magnet over the entire displacement path of the valve piston.

The known partially generic valve devices require path sensors and analysis and control electronics. They are thus overall complex in structure, and disturbances in operation are possible.

DE 102 24 739 A1 discloses a valve device of the initially named type. In the known valve device, the pilot valve and the pilot chamber are each located in a control cover which is located on a side surface of the valve housing. The object of providing a valve control apparatus that requires little installation space in the longitudinal direction of the control valve is achieved here in that the pilot valve and/or the actuator are arranged perpendicular to the longitudinal axis of the control valve in the control cover. The actuator is located on a side surface of the control cover in this case. There can be an adjusting device of the control valve on an opposite side surface of the control cover.

Proceeding from this prior art, the object of the invention is to devise a valve device which is mechanically simple in structure and enables reliable operation even under adverse operating conditions.

This object is achieved with a valve device having the features specified in claim 1 in its entirety.

At least one, preferably each pilot piston according to the invention has on its outer periphery a ring channel. The ring channel enables a connection of a pilot chamber-side supply channel of pilot oil to a channel for discharging pilot oil to the respective tank connection of each pilot valve. When the pilot control unit is opened such that pressure medium or pilot oil travels from the pilot chamber via the ring channel to a tank connection, a pressure drop occurs on the back of the valve piston, and the valve piston is moved in the opposite direction since the other pilot chamber remains at the pump pressure level so that the valve piston is moved in the direction of the respective electromagnet by the pressure imbalance which is being established in the pilot chambers.

From the respective pilot chambers, fluid-conducting connections advantageously, in the form of narrow longitudinal channels with one branch duct each—which is kept short in length—lead to the ring channel which is located on the respective outer peripheral surface of each pilot piston. Coining from the pilot chambers to the fluid-conducting connections, each tank connection preferably includes other branch ducts and longitudinal channels which are diametrically opposite the shorter branch ducts in the valve housing and which lead to the respective tank connection in the valve housing. The magnetic force of the respective electromagnet moves the pilot piston such that the ring channel on its outer peripheral surface covers the two branch ducts. With this valve arrangement, a piloted directional valve is implemented which enables the indicated fluid-conducting connections at very low pilot pressure.

When the electromagnet assigned to the first pilot piston is actuated, the pertinent pilot piston opens the fluid-conducting connection between the first pilot chamber and the tank connection. Pressure medium from the first pilot chamber can escape into a pressure medium tank. As a result, the valve piston is moved by the force of the system pressure of the pressure connection into the second pilot chamber in the direction of the first pilot piston which is moving toward the valve piston, and a corresponding load connection is joined to the pressure connection. Another load connection is joined to the tank connection. The pilot piston is made in the manner of a sliding piston so that each pilot valve is designed as a valve, preferably without a gasket. Obstructive friction in operation is thus minimized, and it is furthermore ensured that the respective pilot valve can perform its throttling function undisturbed.

A possible deleterious effect on the valve piston by forces of friction or flow can be compensated without control effort by an intensified outflow of the pressure medium from the first pilot chamber, as a result of which the valve piston continues to move in the direction of the desired position. When the electrical current for the first electromagnet is lowered or turned off, the pilot piston moves, preferably in addition caused by an energy storage mechanism, in the direction of a blocking position of the fluid-conducting connection between the first pilot chamber and the tank connection. The pressure that builds up again in the first pilot chamber moves the valve piston again in the direction of its rest position.

The valve piston can also be axially displaced in the same described manner into the opposite direction when the second electromagnet is energized. In this way, the second load connection can be connected to the pressure connection and the first load connection to the tank connection. There is continuously a fluid-conducting connection between the pressure connection and the first and second pilot chamber. The pressure medium in the pilot chambers can act directly on the respective back side of the valve piston.

In one preferred embodiment of the valve device according to the invention, the respective pilot chambers are connected to conduct fluid to branch ducts which, penetrating the valve housing in the radial direction, are connected to a common pressure connection bore which, in the axial direction of the valve housing, extends preferably to its two free face sides. Especially preferably, the branch ducts and the pressure connection bore form a first and second fluid-conducting connection for the two pilot chambers and can be charged with the control or pump connection pressure. An internal pressure balance between the two pilot chambers is thus attained as well as delivery of the desired pressure, which can be easily implemented.

In one preferred embodiment of the valve device according to the invention, one compression spring at a time is provided between the valve piston and each pilot piston, with the stroke of the valve piston being proportional to the magnet current of the magnet apparatus with the pilot control unit open. The compression spring, which is acting on the valve piston, signals the position of the valve piston back to the respective pilot piston so that possible disruptive variables, for example, caused by flow forces, can be immediately corrected. The position of the valve piston is moreover directly correlated to the applied magnet current. On the free end of the compression spring, which is facing the assigned pilot piston, there is a stop piece which is connected to the free end of the respective pilot piston in turn via a stop ball.

The stop ball allows unobstructed operation when the pilot piston and valve piston are interacting.

In one especially preferred exemplary embodiment of the valve device, the assigned electromagnet acts on the respective pilot piston with thrust in the direction of the valve piston as soon as the electromagnet is energized. As a result, the fluid-conducting connection from the respective pilot chamber via the ring channel on the respective pilot piston is opened to the respective tank connection.

There is one further compression spring at a time which is supported on the one hand on a valve housing shoulder and on the other hand on a radial widening of the pilot piston in order to thereby bring the pilot piston with its radial widening into contact with a stop flange of the valve housing. In the unenergized state of each electromagnet, there is thus a closed position of the pilot piston and, accordingly, its ring channel between the respective pilot chamber and the tank connection. The connecting channels which constitute the fluid-conducting connection between the respective pilot chambers and the respective tank connection via the respective ring channel on the pilot pistons are formed in the valve housing as longitudinal channels and branch ducts which run transversely thereto.

The valve piston is held in a neutral position by an energy storage mechanism acting with the same pressure force in addition to the same pressure force of the pressure medium in the pilot chambers on both back sides of the piston. The two energy storage mechanisms can be compression springs. In order not to tap the supply pressure directly from the pressure connection, it can be advantageous to connect the pressure connection and thus the fluid-conducting connections from the pressure connection to the pilot chambers at the same time by one load connection which represents the load side of the load via a shuttle valve. This means that it is also possible to operate the valve arrangements with the pressure medium pump turned off, solely by the load pressure on the consumer. When the pressure medium pump is turned on again, the shuttle valve blocks, and the pressure on the pressure connection is transferred directly from the pump to the two pilot chambers.

In order to route the available pressure which is the highest at the time either from the pressure connection or the two load connections in the load circuit to the pilot chambers as a pilot pressure, all three pertinent connections, specifically the pressure connection, first load connection, and second load connection, can be connected via one nonreturn valve at a time to a collecting line to the fluid-conducting connection to the pilot chambers.

To center the valve piston in its neutral middle rest position in the piston bore and to return the valve piston when it is deflected, in addition one energy storage mechanism at a time or especially one compression spring can be inserted into each pilot chamber.

A symmetrical embodiment of the valve device, which is therefore easy to fabricate, is produced by selecting a middle position of the pressure connection of the pressure medium pump with reference to the longitudinal axis of the valve housing. To both sides of the pressure connection, the first and second load connection and a first and second tank connection are connected to the pressure connection with respectively preferably the same distance. A pressure connection for pressurizing the pilot chambers can be separately provided on the valve housing and can branch to the two pilot chambers.

Hereinafter, the valve device according to the invention is detailed using various embodiments as shown in the drawings. The figures are schematic and not to scale.

FIG. 1 shows a longitudinal section through a first embodiment of the valve device according to the invention;

FIG. 2 shows a longitudinal section through a further second embodiment of the valve device according to the invention;

FIG. 3 shows a longitudinal section through a further third embodiment of the valve device according to the invention;

FIG. 4 shows an enlarged detail circumscribed in FIG. 1 marked with the numeral IV.

FIG. 1 and, according to the detail in FIG. 4, in a schematic longitudinal section, which is not to scale, shows a valve device 1 for controlling pressure media, such as hydraulic oil, to a load which is not detailed. The valve device 1 has a valve housing 2 which is made essentially cylindrical. A through bore which is designed as piston bore 3 or guide cylinder for a valve piston 4 is made in the valve housing 2 for this purpose. For indirect actuation of the valve piston 4, on both sides of the valve housing 2, a first and second electromagnet 5, 6 are mounted in one centering bore at a time in the valve housing 2 in a manner which is not shown. The electromagnets 5, 6 are designed as proportional solenoids. In the valve housing 2, fluid connection sites are furthermore made in the form of at least one pump connection or pressure connection P, two load connections A, B, and two tank connections T1, T2. The valve piston 4, which is guided to be able to move lengthwise in the valve housing 2, has projections 27, 28 which are radial on the outer peripheral side. The respective radial outer periphery of the respective projection is chosen such that it can slide sealingly on the inner peripheral side of the piston bore 3.

In the exemplary embodiments of FIGS. 1 to 4, the two middle projections 27 are assigned to the load connections A, B, and the two projections 28, which are located axially on the ends of the valve piston 4, are assigned to the tank connections T1 and T2. Between the projections 27, 28, the valve piston 4 is reduced in diameter so that fluid-conducting paths are formed between the inner periphery of the valve housing 2 and the respectively reduced outside diameter of the valve piston 4.

On its two opposite sides, the valve housing 2 has one first pilot control unit 7 at a time with a first pilot chamber 8 and a second pilot chamber 10 whose respective volume can be changed by means of the movable valve piston 4. The respective pilot chambers 8, 10 are connected to conduct fluid to the branch ducts 29, 30 which, extending through the valve housing 2 in the radial direction, are connected to a common pressure connection bore 31 which extends in the axial direction through the valve housing 2 to its two free face sides. The branch ducts 29, 30 and the pressure connection bore 31 form a first and second fluid-conducting connection 12, 13 for the two pilot chambers 8, 9 and are supplied with the control or pump connection pressure P.

The pilot control unit 7 itself is made in the manner of a spool valve 18 in which a first and second pilot piston 14, 15 are guided to be able to move longitudinally in the valve housing 2 in a corresponding longitudinal bore 32 which is circular in cross section and which has a smaller diameter than the longitudinal bore 3 for the valve piston 4. Each pilot piston 14, 15 is surrounded on the outer peripheral side by pressure relief grooves which at least partially ensure the absence of leaks in this axial region for the pilot pistons 14, 15 and hence form a type of sealing system 26. Otherwise, the pressure relief grooves shorten the effective gap length of the sealing gap and therefore reduce the tendency to sticking.

Viewed in the longitudinal direction of the valve arrangement 1, the pilot chamber 8,10 is located between one piston back side 9, 11 at a time of the valve piston 4 and a valve insert 34 which holds the electromagnets 5, 6, which pilot chamber is connected to the respective end of the valve piston 4. From the respective pilot chambers 8, 10, other fluid-conducting connections 16, 17, first in the form of narrow longitudinal channels 35 with one radial branch duct 36 at a time, which is kept very short in length, lead to a ring channel 19 located on the respective outer peripheral surface 20 of each pilot piston 14, 15.

Coming from the pilot chambers 8, 10 to the fluid-conducting connections 16, 17, one tank connection T1, T2 at a time includes other branch ducts 37 and longitudinal channels 38 which are diametrically opposite the shorter branch ducts 36 in the valve housing 2 and which lead to the respective tank connection T1, T2 in the valve housing 2.

The valve piston 4 is in its closed operating position in FIGS. 1 to 4.

The valve piston 4 has a pin-like extension 39 which is smaller in diameter than its other diameter. The extension 39, which is formed on both ends of the valve piston 4 integrally with the valve piston 4, projects axially as far as approximately to the middle of the respective pilot chambers 8, 10. Each extension 39 projects through a stop disk 40 of a respective stop piece 23. The respective stop piece 23 on its end facing away from the respective extension 39 has a disk-like widening which bears one stop ball 22 at a time in a corresponding recess. The free end of each pilot piston 14, 15 is supported in this case on the stop ball 22. In this way, unobstructed operation and triggering between pilot pistons 14, 15 and the valve piston 4 are achieved even in the event that sticking processes were to occur which can then be compensated by the stop ball 22. Hydrodynamic damping can be implemented via the extension 39 in conjunction with the respective stop piece 23. If damping should not be required for the application, the component 23 is made simply as a spring cup. This sleeve is then made shorter in order not to place it over the piston.

There is one compression spring 21 at a time between the valve piston 4 and the stop piece 23. The helical cylinder-like compression spring 21 is supported on the one hand in a first end-side annular groove 42 of each stop disk 40. On the other hand, the respective compression spring 21 is supported on the respective disk-like end of the stop piece 23. The compression spring 21 has a smaller diameter than one other compression spring 25 which is supported on the stop disk 40 and on the respective valve insert 34. The compression spring 25 is centered in an annular groove 43 in the stop disk 40 and in an annular groove 44 which is located on the free end of the valve insert 34. It radially surrounds the respective compression spring 21. The indicated compression spring 25 presses the stop disk 40 against a narrowing of the diameter 45 of the pilot chamber 8, 10 and against the respective end surface 46 out of which the extension 39 projects. This arrangement results in a precisely reproducible neutral position for the valve piston 4.

There is one other third compression spring 24 at a time to move the respective pilot position 14, 15 into a “closed position.” For this purpose, there is an annular space 47 in the valve insert 34. The respective compression spring 24 is supported on a bottom 48 of the respective annular space 47 and on a radial widening 49 of the respective pilot piston 14, 15. In this way, the respective compression spring 24 presses the radial widening 49 against a respective stop collar 50 of a screw base via which the respective electromagnet 4, 5 is screwed into the respective valve insert 34. The free end 51 of the respective pilot piston 14, 15 is in contact with one free end of an actuating plunger 52 of each electromagnet 5, 6.

For the sake of better understanding, the operation of the exemplary embodiment of a valve arrangement according to the invention as shown in FIG. 1 is detailed with respect to the pilot control unit.

When the electromagnet 5 is energized, a magnet armature, which is not detailed, migrates under the action of the field of a coil winding, which is not shown, and thus also the actuating plunger 52 out of the pole tube of the magnet apparatus to the right as seen in the direction of viewing. As a result, the pilot piston 14 experiences a thrust opposite the action of the compression spring 24 and of the compression spring 21, which tend, with their reset forces, to keep the radial widening 49 in contact with the stop collar 50. The indicated magnetic force is sufficient to move the pilot piston 14 opposite the action of the compression springs 21, 24 such that the ring channel 19 on its outer peripheral surface 20 covers the branch duct 36 and the branch duct 37. The pilot control unit 7 is thus opened such that the pressure medium or pilot oil travels from the pilot chamber 8 via the longitudinal channel 38 to the tank connection T1. At the same time, the pressure on the back side 9 of the valve piston 4 drops, and the valve piston 4 is moved against the action of the compression spring 21 to the left, viewed in the direction of looking at FIG. 1, since the second pilot chamber 10 remains at the pump pressure level P so that the valve piston 4 is moved in the direction of the first electromagnet 5 in the pilot chambers 8, 10 by the pressure imbalance which is being established. The longitudinal bore which is shown by the broken line in the figures in the valve insert 34 establishes the pressure equalization between the pilot chamber and pole tube so that the pilot piston 14 is in an equilibrium of forces.

This piston stroke of the valve piston 4 is proportional to the magnetic force of the electromagnet 5. The compression spring 21 signals the position of the valve piston 4 back to the pilot piston 4 so that disruptive variables, such as, for example, flow forces, can be corrected in this way, and the position of the valve piston 4 thus always corresponds to the magnetic force of the electromagnet 5 in the energized state.

When power to the first electromagnet is reduced or cut off, the valve piston 4 returns to its initial position under the action of the compression springs 21 and 25. The same sequence in the reverse direction takes place when the second electromagnet 6 is energized. The load connection B becomes connected to the tank connection T2 to conduct fluid, and the load connection A becomes connected to the pressure connection P to conduct fluid.

With this valve arrangement 1, a pilot-actuated directional valve is therefore implemented which at very low pilot pressure already enables the indicated fluid-conducting connections. The compression spring 21 is not critically necessary; it does, however, improve the return of the pilot piston 14, 15 and thus overall the dynamics for the valve arrangement 1. In particular, the compression spring 21 is used for feedback of the piston position as a force back to the magnet system. The implemented pilot control unit 7 is made in the manner of a spool valve, it being the best solution to the uniform actuating behavior under different operating conditions and pressure characteristics.

As FIG. 2 in particular shows, the supply pressure for the two pilot chambers 8, 10 can be tapped not only from the pressure connection P, but also via a coupling of the load connections A, B and of the pressure connection P with interposition of a shuttle valve W either directly from the pressure connection P or one of the load connections A, B, before the pressure medium is supplied to the pilot chambers 8, 10. This design measure allows the valve device to be operated even with the pressure medium pump turned off.

As shown by FIG. 3 in particular, it can be advantageous to tap the highest available pressure medium pressure by a parallel connection of the indicated connections P, A, B via one nonreturn valve 53, 54, 55 respectively which opens in the direction of the pilot chambers 8, 10 between the connections.

The valve device 1 which is piloted in this way does not require any path sensors for the valve piston 4, nor are further analysis and control electronics critically necessary either. The valve device 1 thus has a simple structure and low susceptibility to faults based on its mechanical design. When the current supply to the electromagnets 5, 6 is cut off, for example, in the case of damage, the valve piston 4 automatically returns to its spring-centered, blocking middle position. 

1. A valve device comprising a valve housing (2) and a valve piston (4) which is arranged to be able to move axially in a piston bore (3) of the valve housing (2) and via which a first load connection (A) and a second load connection (B) can be alternately connected to a pressure connection (P) and to a tank connection (T1, T2) by the action of a first electromagnet (5) and a second electromagnet (6), and the valve piston (4) can be moved out of a centered middle rest position for connecting the first load connection (A) to the pressure connection (P) and the second load connection (B) to the tank connection (T1, T2) in a first direction and for the reversed fluid-conducting connection of the connections (A, B, P, T1, T2) can be moved in an opposite direction, there being a pilot control unit (7) which has a first pilot chamber (8) which pressurizes a first piston back side (9) of the valve piston (4) and which has a second pilot chamber (10) which pressurizes a second piston back side (11) of the valve piston (4), and the first and second pilot chamber (8, 10) with one fluid-conducting connection (12, 13) each can be connected to the pressure connection (P), there being a first pilot piston (14) and a second pilot piston (15) which clear or block one fluid-conducting connection (16, 17) at a time between the pilot chambers (8, 10) and the tank connection (T1, T2), and the pilot control unit (7) being made in the manner of a spool valve (18), characterized in that at least one pilot piston (14, 15) has a ring channel (19) on its outer peripheral surface (20) which controls a fluid-conducting connection (16, 17) between the respective pilot chamber (8, 10) and the respectively assigned tank connection (T1, T2).
 2. The valve device according to claim 1, characterized in that from the respective pilot chambers (8, 10), fluid-conducting connections (16, 17) in the form of narrow longitudinal channels (35) with one radial branch duct (36) each, which is kept short in length, lead to the respective ring channel (19).
 3. The valve device according to claim 2, characterized in that, coming from the pilot chambers (8, 10) to the fluid-conducting connections (16, 17), one tank connection (T1, T2) at a time includes other branch ducts (37) and longitudinal channels (38) which are opposite the shorter branch ducts (36) and which lead to the respective tank connection (T1, T2) in the valve housing (2).
 4. The valve device according to claim 1, characterized in that the respective pilot chambers (8, 10) are connected to conduct fluid to branch ducts (29, 30) which, penetrating the valve housing (2) in the radial direction, are connected to a common pressure connection bore (31) which in the axial direction of the valve housing (2) extends preferably to its two free face sides.
 5. The valve device according to claim 4, characterized in that the branch ducts (29, 30) and the pressure connection bore (31) form a first and second fluid-conducting connection (12, 13) for the two pilot chambers (8, 10) and can be supplied with the control or pump connection pressure (P).
 6. The valve device according to claim 1, characterized in that there is a compression spring (21) between the valve piston (4) and each pilot piston (14, 15) and the piston stroke of the valve piston (4) is proportional to the magnet current of the triggering electromagnet (5, 6) when the pilot control unit (7) is open.
 7. The valve device according to claim 1, characterized in that there is a stop ball (22) which connects the pilot piston (14, 15) to the stop piece (23) of the valve piston (4) on one free end of each pilot piston (14, 15).
 8. The valve device according to claim 7, characterized in that the stop piece (23) adjoins the valve piston (4) with interposition of the compression spring (21).
 9. The valve device according to claim 1, characterized in that a thrust force can be applied to the respective pilot piston (14, 15) by the respectively assigned electromagnet (5, 6) in order to effect opening of the fluid-conducting connection (16, 17) from the respective pilot chamber (8, 10) to the assigned tank connection (T1, T2).
 10. The valve device according to claim 1, characterized in that there is one compression spring (24) at a time to move the respective pilot piston (14, 15) into a closed position of the pilot control unit (7).
 11. The valve device according to claim 1, characterized in that there is one compression spring (25) at a time on the ends of the valve piston (4) in order to keep the valve piston (4) in a neutral position.
 12. The valve device according to claim 1, characterized in that the fluid-conducting connection (16, 17) is located between each pilot chamber (8, 10) and the assigned tank connection (T1, T2) in the valve housing (4).
 13. The valve device according to claim 1, characterized in that the pilot chambers (8, 10) can be connected to a load connection (A, B) or the pressure connection (P) with interposition of a shuttle valve (W). 